I'm installing railings at the shallow-end steps and deep-end stairs of our pool. There are fasteners/clamps that slide into the housing built into the concrete where the railing pole slides in, then the fastener is screwed down to securely keep the railing in place. My pics do a much better job of explaining/showing what I'm in search of. I'm missing a few of these fastenerss/clamps. Can anyone help with where to buy these fasteners/clamps? Or does anyone know what they're called to help with a Google search or pool store inquiry. I'm sure they're old, as my pool was installed in late 80s / early to mid 90s. Thanks for any feedback.